The field of the disclosure relates generally to gas turbine engines and, more particularly, to a centerline-mounted hydraulic pitch change mechanism actuator.
At least some known aircraft include gas turbine engines, which include a power turbine driving counter-rotatable propeller rotors. The power turbine is powered by a gas generator. The rotors drive a set of fan blades. The pitch of these fan blades facilitates control of the thrust of the engine. At least some known engines include multiple actuators configured to control the pitch of individual blades. In such systems, movement of the blades may not be uniform or simultaneous, which may decrease the efficiency of such a system, and such systems may be quite complex. Moreover, some known systems provide one or more actuators (or other pitch change mechanisms) that are asymmetrically disposed about an engine centerline of the engine, which may necessitate more complex or additional bearing interfaces.
Some known pitch control mechanisms include counterweights configured to affect the position or pitch of the blades, particularly in low fluid-pressure conditions. At least some of these systems mount the counterweights directly to blade-retention components. Such an arrangement may be problematic for fan assemblies with low fan hub radius ratios, because counterweight effectiveness is based on distance of a counterweight to a blade pitch change axis. As space between adjacent blades becomes limited at the hub, counterweights may be very heavy and inefficient. Alternatively, some known variable pitch fan systems use a pitch-lock system, which retains each blade at the angle the blade had when the pitch change mechanism lost adequate fluid pressure. If neither a counterweight nor a pitch-lock system is included, the blades could swing to a “fine” position in the event of loss of fluid pressure, which can unload a load torque on the turbine driving the fan.